This invention relates to a speed controller for a marine propulsion device and more particularly to an improved control arrangement for maintaining the speed of an internal combustion engine within a preset range.
In many devices powered by internal combustion engines, the operator has a speed control which he sets so as to select the running speed of the engine. However, the actual running speed of the engine can vary considerably from the preset speed due to variations in running conditions and other factors. For example, when considering a watercraft propelled by an internal combustion engine, the operator normally sets the engine running speed with a throttle or throttle lever of some type. However, even though the operator selects an appropriate speed for certain conditions, the actual speed of the engine may vary considerably due to a variety of factors. For example, as the propeller becomes worn, the speed of the engine may increase above that desired by the operator and, in fact, above that which is safe for engine operation. Also, a variety of transient conditions can cause the engine to speed up or slow down from the value set by the operator. Therefore, it is necessary for the operator to keep a vigilant eye on the tachometer so as to prevent overspeeding of the engine and resulting damage.
It is, therefore, a principal object of this invention to provide an improved speed control mechanism for an internal combustion engine.
It is another object of this invention to provide a speed control mechanism for a marine propulsion device wherein the running speed of the engine is maintained at a substantially constant value regardless of variations in external conditions.
It is a further object of this invention to provide a speed control for a marine propulsion device wherein the speed control does not interfere with the normal throttle operation of the engine.
In conjunction with a speed control constructed in accordance with an embodiment of the invention, a device is provided for sensing differences between desired engine speed and actual running speed. This sensing device controls a throttle mechanism so as to maintain the engine running speed at the preset speed. Although such an arrangement is particularly advantageous, a device that merely senses speed differences and compensates for them may cause excessive hunting of the throttle position, may be subject to undue wear and may, under some conditions, adversely affect the performance under acceleration.
It is, therefore, a still further object of this invention to provide an improved control for a speed control device that minimizes undesirable hunting and the like.